I'm not sure if you mean that 6pt type should have 6.1 pt leading and 7 pt type should have 7.1 leading, in which case the only way to set it is manually in a style, or if you mean you want the value to change by .1 when you nudge it.
If the latter, you can set the value you wish to use in the Preferences under Units and Increments. This will not affect the nudge buttons in the Control panel or Character panel, but it will affect the amount of change when you use the keyboard shortcuts (Alt/Opt plus the up or down arrows, by default).